Non-Volatile Memory With Linear Estimation of Initial Programming Voltage

Abstract

In a non-volatile memory, a selected page on a word line is successively programmed by a series of voltage pulses of a staircase waveform with verifications in between the pulses until the page is verified to a designated pattern. The programming voltage at the time the page is programmed verified will be to estimate the initial value of a starting programming voltage for the page. The estimation is further refined by using the estimate from a first pass in a second pass. Also, when the test is over multiple blocks, sampling of word lines based on similar geometrical locations of the blocks can yield a starting programming voltage optimized for faster programming pages.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is related to the following U.S. patent applications: U.S. application Ser. No. ______, entitled “Method For Non-Volatile Memory With Reduced Erase / Write Cycling During Trimming Of Initial Programming Voltage,” by Yan Li, et al., filed concurrently herewith, on Sep. 12, 2006. U.S. application Ser. No. ______, entitled “Non-Volatile Memory With Reduced Erase / Write Cycling During Trimming Of Initial Programming Voltage,” by Yan Li, et al., filed concurrently herewith, on Sep. 12, 2006. U.S. application Ser. No. ______, entitled “Method For Non-Volatile Memory With Linear Estimation Of Initial Programming Voltage,” by Loc Tu, et al., filed concurrently herewith, on Sep. 12, 2006.FIELD OF THE INVENTION[0002]This invention relates generally to non-volatile semiconductor memory such as electrically erasable programmable read-only memory (EEPROM) and flash EEPROM, and specifically to determining optimum initial programming volta...

AI Technical Summary

Benefits of technology

[0021]One advantage of this scaling scheme is that a simple one- or two-pass programming test on each page / word line is sufficient to yield an estimate for the starting programming voltage for the page. Each page can be tested independently and does not involve multiple erase operation during the test. Therefore there is no need for management of block erase among a sample of word lines.VPGM Trimming Weighted Toward Faster Programming Pages

[0023]The scheme of testing individual samples formed by selecting at least a similar page from each block also has the advantage of minimum storage requirement. After each sample is tested, a test result in the form of an average is obtained and stored. Then the next sample is tested in similar manner and its average is then compared to the first one in storage. Whichever average is the lower one will be retained in storage so that only one data need be stored as the set of samples is processed a sample at a time.

[0025]Also, with the sample formed by selecting a relatively small portion from each of the blocks, another advantage is that the sample average is not as sensitive to the presence of any bad blocks where a large portion of the word lines in it may be defective.

Problems solved by technology

Conventional mass storage, based on rotating magnetic medium such as hard drives and floppy disks, is unsuitable for the mobile and handheld environment.

This is because disk drives tend to be bulky, are prone to mechanical failure and have high latency and high power requirements.

These undesirable attributes make disk-based storage impractical in most mobile and portable applications.

If the initial programming voltage VPGM0 is chosen too low, it may require an excessive number of programming pulses to reach the target state.

On the other hand if VPGM0 is chosen too high, especially in a multi-state memory, the programming may overshoot the target state in the first pulse.

Conventional VPGM0 trimmings are therefore performed by memory testers that are expensive dedicated machines.

Non-volatile memory device has a limited life usage due to the endurance-related stress suffered each time the device goes through an erase / program cycle.

The physical phenomenon limiting the endurance of non-volatile memory devices is the trapping of electrons in the active dielectric films of the device.

Thus, conventional VPGM trimmings at the factory could consume as much as several thousand endurance cycles of a memory device.

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